1. Field of the Invention
The present invention relates to a method and an apparatus for estimating a spectral reflectance distribution or a spectral transmittance distribution suitable for a device-independent color reproduction method and apparatus in, for example, color DTP. More particularly, the present invention concerns a method and an apparatus for estimating a spectral reflectance distribution or a spectral transmittance distribution, which are necessary as a color reproduction process to ensure that the appearance of a color reproduced by any color reproducing apparatus always becomes the appearance of the color of an original by being not only device-independent but illuminant-independent, by using characteristic parameters which are obtained by the multivariate analysis of the spectral reflectance distribution or the spectral transmittance distribution and which are always capable of accurately representing the physical properties of the color irrespective of the kind of illuminant as a device-independent color representation process.
2. Description of the Related Art
A so-called device-independent color reproduction method is conventionally known as a method of color reproduction in which the reproduced color is not dependent on a device and which is capable of reproducing the same color as that of an original even if the color is reproduced by any device. In this device-independent color reproduction method, color information is temporarily transformed into representations which are not dependent on the device, and color correction is then carried out.
In the above-described reproduction method, the same color as that of an original is reproduced with high accuracy without being dependent on the device, by representing the color of the original by using calorimetric values, such as CIE L*a*b*, CIE L*u*v* uniform color space, or CIE XYZ values prescribed by CIE (Commission Internationale de l'Eclairage), and then by effecting transformations between the calorimetric values and device values such as CMYK values.
However, since the CIE L*a*b*, CIE L*u*v*, CIE XYZ values, or the like are defined by the spectral distributions of illuminants, spectral reflectance distributions of the subject surfaces, and color matching functions, the above-described conventional device-independent color reproduction method has a problem in that the reproduced color does not match the color of the original unless the illuminant used for observing the color of the original is the same as the illuminant used in deriving the CIE L*a*b* values or the like.
As described above, the conventional device-independent color reproduction method has the problem that the illuminants allowing the reproduced color to appear to be the same color as the original are restricted, color matching cannot be accomplished only under very limited environments, i.e., illumination.
Meanwhile, there are various types of illumination used for observation of colors, including illumination under an incandescent lamp, illumination under a fluorescent lamp, sunlight, and so on. Therefore, the conventional device-independent color reproduction method disadvantageously makes it impossible to allow the reproduced color to always match the color of the original under such illuminants.